[#8951] - Small font size after Importing a report created with iReport 5.1.0 to Jaspersoft Studio 5.6.1 and compiling it

I have some reports created with iReport 5.1.0 and because the software is really slow, especially when the report has more than one (1) detail section, I switched to Jaspersoft Studio v5.6.1. The reports are generated using a java servlet. The jar files I use are:
- commons-beanutils-1.8.0.jar
- commons-collections-2.1.1.jar
- commons-digester-2.1.jar
- commons-javaflow-20060411.jar
- commons-logging-1.1.1.jar
- iText-2.1.7.js2.jar
- jasperreports-5.1.0.jar
- jfreechart-1.0.12.jar

When I compile my reports usng JS Studio and create the PDF files, the fonts are much smaller than on the design. On the other hand, when I compile the reports using iReport 5.1.0 and print the PDF files, they appear normal.
I tried to switch from jasperreports-5.1.0.jar to jasperreports-6.3.1.jar but I cannot figure out what *.jars I need. I tried with jasperreports-6.3.1.jar, jasperreports-fonts-6.3.1.jar and jasperreports-javaflow-6.3.1.jar but every time I got runtime Exceptions like ClassNotFound.
The font I am using is Calibri.

Can anyone give me some feedback ?